1. Field of the Invention
Aspects of the invention relate to a switching mode power supply apparatus and a power supply method thereof, and more particularly to a switching mode power supply apparatus that detects a voltage of power applied to a light receiving unit and a power supply method thereof.
2. Related Art
A switching mode power supply apparatus rectifies AC power received from an external power source to obtain DC power, converts the DC power into AC power by performing a switching operation, changes a voltage of the AC power using a transformer, and rectifies and smoothes the transformed AC power, thereby outputting smoothed DC power. The foregoing process is widely used because it decreases power loss and heat generation compared to a linear power supply apparatus that converts AC power into DC power using a passive element, such as a voltage-dividing resistor.
Referring to FIG. 1A, a switching mode power supply apparatus 1 according to the related art includes a conversion unit 2 that converts input power into output power having a predetermined voltage by performing a switching operation. An output unit 3 outputs the output power to an external device (not shown). A light emitting unit 4 emits light if the voltage of the output power exceeds a predetermined threshold voltage. A light receiving unit 5 receives light from the light emitting unit 4 and outputs a signal indicative of the voltage of the output power. A switching controller 6 controls the switching operation of the conversion unit 2 according to the voltage of the output power indicated by the signal output from the light receiving unit 5.
FIG. 1B is a detailed circuit diagram of a portion of the switching mode power supply apparatus 1 of FIG. 1A according to the related art. External AC power (e.g., an AC voltage of 220 V) is applied to a drain terminal of a metal-oxide semiconductor field effect transistor (MOSFET), a pulse-width modulated signal is generated based on the voltage of the output power indicated by the signal output from the light receiving unit 5 that is applied to a feedback (FB) terminal of the switching controller 6, and the pulse-width modulated signal is output from an output (OUT) terminal of the switching controller 6 and applied to a gate terminal of the MOSFET.
However, if an excessive voltage is applied to the light receiving unit 5 in an abnormal situation (e.g., when a short circuit occurs between the drain terminal of the MOSFET and the FB terminal of the switching controller 6), insulation between the light emitting unit 4 and the light receiving unit 5 may be destroyed. Such an abnormal situation is more likely to occur when the MOSFET and the switching controller 6 are integrated in a single device. If the insulation is destroyed, a voltage applied to the light emitting unit 4 will be transmitted to the light receiving unit 5, which may injure a user.